CHAPTER 42 - Thorium

Abstract

This chapter discusses the methods for the determination of thorium from silicate rock. Ion-exchange column chromatography, solvent extraction, and precipitation methods are used for the separation of thorium. However, none of these methods gives a complete separation in a single operation. Therefore, a number of authors recommend combinations of two or more procedures. The chapter discusses the spectrophotometric determination using a fluoride precipitation. The silicate material is decomposed by evaporation with hydrofluoric acid and nitric acid. Thorium, rare earths, and calcium are precipitated together as fluorides after the addition of a calcium carrier solution. Precipitations with potassium hydroxide and potassium iodate are used to complete the separation of thorium from other elements before photometric determination with arsenazo III. The chapter also describes the spectrophotometric determination of thorium using an anion-exchange separation. In the procedure, after the decomposition of the silicate material, fluorine is complexed with boric acid and the nitrate solution transferred to a strongly basic anion exchange resin. The resin is washed with diluted nitric acid to remove interferring elements and thorium is recovered by elution with hydrochloric acid.